An organic EL device is a spontaneous light emitting device which utilizes the principle that a fluorescent substance emits light by energy of recombination of holes injected from an anode and electrons injected from a cathode when an electric field is applied. Since an organic EL device of the laminate type driven under a low electric voltage was reported by C. W. Tang et al. of Eastman Kodak Company (C. W. Tang and S. A. Vanslyke, Applied Physics Letters, Volume 51, Pages 913, 1987 or the like), many studies have been conducted on organic EL devices using organic materials as the constituent materials. Tang et al. used tris(8-quinolinolato)aluminum for a light emitting layer and a triphenyldiamine derivative for a hole transporting layer. Advantages of the laminate structure are that the efficiency of hole injection into the light emitting layer can be increased, that the efficiency of forming exciton which are formed by blocking and recombining electrons injected from the cathode can be increased, and that exciton formed within the light emitting layer can be enclosed. As described above, for the structure of the organic EL device, a two-layered structure having a hole transporting (injecting) layer and an electron-transporting light emitting layer and a three-layered structure having a hole transporting (injecting) layer, a light emitting layer, and an electron-transporting (injecting) layer are well known. To increase the efficiency of recombination of injected holes and electrons in the devices of the laminate type, the structure of the device and the process for forming the device have been studied.
In general, when an organic EL device is driven or stored in an environment of a high temperature, adverse effects such as a change in the luminescent color, a decrease in emission efficiency, an increase in the voltage for driving, and a decrease in the lifetime of light emission arise. To prevent the adverse effects, it has been necessary that the glass transition temperature (Tg) of the hole transporting material be elevated. Therefore, it is necessary that the many aromatic groups be held within the molecule of the hole transporting material, for example, the aromatic diamine derivative in Patent Document 1 and the fused aromatic ring diamine derivative in Patent Document 2, and in general, a structure having 8 to 12 benzene rings may preferably be used.
However, when a large number of aromatic groups are present in a molecule, crystallization is apt to occur upon production of an organic EL device through the formation of a thin film by using those hole transporting materials. As a result, there arises a problem such as the clogging of the outlet of a crucible to be used in vapor deposition or a reduction in yields of the organic EL device due to the generation of a fault of the thin film resulting from the crystallization. In addition, a compound having a large number of aromatic groups in any one of its molecules generally has a high glass transition temperature (Tg), but has a high sublimation temperature. Accordingly, there arises a problem in that the lifetime of the compound is short because a phenomenon such as decomposition at the time of vapor deposition or the formation of a nonuniform deposition film is expected to occur.
Meanwhile, there is a known document disclosing an asymmetric aromatic amine derivative. For example, Patent Document 3 describes an aromatic amine derivative having an asymmetric structure. However, the document has no specific example, and has no description concerning characteristics of an asymmetric compound. In addition, Patent Document 4 describes an asymmetric aromatic amine derivative having phenanthrene as an example. However, the derivative is treated in the same way as that of a symmetric compound, and the document has no description concerning characteristics of an asymmetric compound. In addition, none of those patents explicitly describes a method of producing an asymmetric compound in spite of the fact that the asymmetric compound requires a special synthesis method. Further, Patent Document 5 describes a method of producing an aromatic amine derivative having an asymmetric structure, but has no description concerning characteristics of an asymmetric compound. Patent Document 6 describes an asymmetric compound which has a high glass transition temperature and which is thermally stable, but exemplifies only a compound having carbazole. In addition, the inventors of the present invention have produced a device by using the compound. As a result, they have found that a problem lies in the short lifetime of the device.
As described above, an organic EL device having a long lifetime has been reported, but it cannot be said yet that the device always shows sufficient performance. In view of the foregoing, the development of an organic EL device having further excellent performance has been strongly desired.    [Patent Document 1] U.S. Pat. No. 4,720,432    [Patent Document 2] U.S. Pat. No. 5,061,569    [Patent Document 3] JP-A-08-48656    [Patent Document 4] JP-A-11-135261    [Patent Document 5] JP-A-2003-171366    [Patent Document 6] U.S. Pat. No. 6,242,115